Data of a single or multiuser computer system is periodically backed up to enable restoration should the data become corrupted or destroyed due to hardware or software failure, or due to inadvertent deletion or change. Backup may be full or partial, and may be carried out at daily, weekly, monthly or other suitable time intervals.
There presently exist many backup utility programs which copy program and data files (collectively encompassed by the term "data"), usually in a compressed mode, from magnetic media hard disks or other data source locations, onto backup media elements such as magnetic tapes or disks sequentially loaded into proximity with a read/write head or similar structure of a tape drive, disk drive or other shared data transfer element. Typically, most backup programs allow backup of an entire disk, or selective backup of a subset of files chosen based upon a variety of file selection criteria, such as file names/extensions or dates of last access, modification, creation, or backup. Some such backup programs further allow the user (or the system administrator) to predefine the file tree and selection criteria so that periodic backups can be easily made without requiring the user to rethink backup strategy each time a backup is made. Recommended backup strategy usually involves making a disk-wide or "baseline" backup of all files at intervals, such as monthly; then making partial or "incremental" backups at shorter, intervening intervals, such as daily or weekly.
Conventional programs provide means for the user to select among available backup targets based upon the separate I/O port addresses of the connected data transfer elements (viz. tape or disk drives). Small backups may sometimes be completed on a single tape or disk media element loaded into the backup destination drive; but, more commonly, the usual backups will require the successive loading and unloading of a plurality of such tape or disk elements into the drive, with data transfer continuing until each media element is filled. The interchange of tapes or disks in the shared backup target drive elements may be effected manually. Larger backup systems, however, often employ a robotic arm or similar automatic media changer mechanism to enable the automatic, unattended interchange of target media elements. Though each tape or disk of a backup device having unattended media element interchange capability has its own predesignated physical location or slot, current implementations of backup media library management systems treat the device as a single target address (viz. address of the shared drive) for data transfer purposes, with the set of physically discrete data storage elements (viz. individual tapes or disks) being interchanged, albeit automatically, in a user-transparent way. Such implementation does not allow for random user access to individual media elements during backup, nor for selection by the user of the media element processing order. In conventional backup schemes, the entire library of media elements is viewed as one, continuous backup destination (one long media device). No single element in the media library is made individually addressable, nor can the elements be grouped and configured into user-designated logical arrangements.
Existing media management library systems, such as the Cheyenne ArcServe v4.0 used with an automatically loading tape drive unit, provide a sequential backup/random restore capability. The backup of data is performed by inserting a magazine containing a series of tape cartridges (set of media elements) into the automatic tape loader, which constitutes the media library device. The user selects the backup source, but cannot specify the backup destination to be a particular tape cartridge or user configurable subset of tape cartridges. The target device is seen as the tape drive itself, not the individual tape cartridges. The backup onto tape media is performed by starting with a first cartridge from the magazine, loading that cartridge for data transfer into the drive. When that tape is full, the first cartridge is unloaded and the second tape cartridge is loaded, and so on. As each tape is used to capacity, the next cartridge is automatically loaded, cascading the data transfer sequentially through the set of cartridges in the library. Such systems treat the set of media elements like a single large media element having a total capacity equal to the sum of the individual media element capacities.
Even though the hardware and communications protocol exist to tell the media changer which slot to go to for the next cartridge, and in what order, conventional backup utility programs make no provision for user-selectable random access to the individual cartridges. Moreover, no provision is made for a user to specify logical groupings of the tape cartridges as destination addresses for data transfer operations.